1. Field of the Invention
The present invention relates generally to electronic component design and, more particularly, to alteration of signal speed on a network signal wire in order to balance skew in the network.
2. Description of Related Art
Currently, most mainstream electronic components and systems, such as microprocessors, are synchronous systems employing one or more system clocks that act as the driving force or xe2x80x9cheartxe2x80x9d of the electronic system. As a result, more often than not, it is critical that a given system clock signal arrive at various points in the system at nearly the same time. As discussed below, this situation can create significant complications in microprocessor design.
FIG. 1 illustrates a portion of a length of signal wire 100 including, from left to right, in the direction shown by arrow 120, points 102, 104 and 106. As is well known, the physics of conductors and wave propagation dictate two precepts: first, the absolute speed limit for any signal moving from point 102 to points 104 or 106 is the speed of light; second, since wire 100 is typically a metallic conductor, with an inherent resistance, a signal propagating in wire 100 actually travels at a speed significantly less than the speed of light.
As a result of these physical limitations on the speed at which a signal can propagate through wire 100, it follows that the greater the distance between two points on/in wire 100, the longer it takes the signal to reach the point. Consequently, a signal traveling from point 102, in the direction shown by arrow 120, will take less time to reach point 104, i.e., travel distance 108, than it will take to reach point 106, i.e., travel distance 108 and distance 110; and thus, there is a time delay between when the signal reaches point 104 and when it reaches point 106. In addition, as can be seen from the discussion above, as long as wire 100 has a reasonably consistent composition and the wire lies on the same metal layer, the time delay is typically proportional to the distance traveled, i.e., twice the distance results in approximately four times the delay.
Typically there are numerous circuit components, located at different distances from the system clock(s) that must receive the clock signal at the same time over interconnecting signal wires. Given the discussion above with respect to FIG. 1, it can be understood that the problem of ensuring a given clock signal is received at a first point and at other variously distanced points, nearly simultaneously, is significant.
One prior art method used to ensure the receipt of a clock signal at the same time at variously distanced points, was to introduce a time delay on the shorter signal paths by forming serpentine signal paths. The introduction of a time delay, also called simply a xe2x80x9cdelayxe2x80x9d, between when one point receives a signal and when a second point, that should receive the signal at the same time, actually receives the signal, is known as skew. When the signal is a clock signal, then it is known as clock skew. Serpentining the signal wire between close points increased the actual length of the signal path over the original distance between the points, and delayed the signal so that the signal arrived at the more distant point at the same time as the close points. Conventionally, serpentining a signal wire involves routing the signal wire in vertical and horizontal directions on the same microprocessor layer using wire jogs.
Although a select signal, such as a clock signal, may need to be delayed in route to a particular component in order to balance skew in the network, optimizing the signal speed in the device is still important in order for the device to remain competitive in the market. To aid in maintaining the integrity and speed of a signal carried on a signal wire, shielding wires are often routed to each side of the signal wire to reduce the effects of electrical noise on the signal wire from other components and signals in the device that can disrupt and delay a signal on the signal wire.
Conventionally, shielding wires are offset a predetermined offset distance from the signal wire to minimize interactions between the shielding wires and the signal wire that could disrupt or delay a signal. Particularly, the shielding wires are positioned at an offset distance to minimize interactions, such as capacitive coupling, between the shielding wires and the signal wire which can result in increased noise and delay on the signal wire. When a signal wire has a serpentine path, typically, the shielding wires follow the serpentine pattern, as needed, at the specified offset distance from the signal wire.
FIG. 2 illustrates a microprocessor clock network having two signal paths issuing from a clock signal source, in which the shorter signal path has a time delay introduced into it by serpentining the signal path. In FIG. 2, microprocessor layer 210 includes clock source 212 that sends clock signals over branched signal wire 220 to two components 214 and 216. Component 214 is located a distance D1 from clock source 212 directly off of signal wire 220 that is shielded by shielding wires 222 and 224. Component 216, however, is located a shorter distance D2 from clock source 212 indirectly off of signal wire 220, namely, off of a portion of signal wire 220 and branch signal wires 230 and 240, and shielded by shielding wires 232 and 234 and shielding wires 242 and 244, respectively. As distance D1 is larger than distance D2, component 214 is farther from clock source 212 than component 216 resulting in a clock skew, e.g., a signal will take longer to reach component 214 than component 216. To ensure the clock signal arrives at both components 214 and 216, nearly simultaneously, signal wire branch 240 is serpentined to increase the actual distance of the signal path to component 216. Thus, the actual signal path length along signal wire branch 240 is longer so as to delay the transit time of a signal to component 216 and balance the clock skew in the network.
While this technique enables the clock signal to arrive at different components, nearly simultaneously, the more complex signal and shielding wire routings can increase the design and process complexity as well as processing time and costs.
According to the principles of this invention, methods and devices for using the coupling capacitance of shielding wires to balance skew in a network are described.
According to one embodiment of the present invention, a method for balancing skew in a network includes: designating a first signal wire in a network, the first signal wire communicatively coupling a sending component with a first receiving component, the first receiving component being located along the first signal wire a first distance from the sending component, the first signal wire carrying a signal sent from the sending component to the first receiving component; designating a second signal wire in the network, the second signal wire communicatively coupling the sending component with a second receiving component, the second receiving component being located along the second signal wire a second distance from the sending component, the second distance being less than the first distance, the second signal wire carrying the signal sent from the sending component to the second receiving component; positioning first and second shielding wires oppositely adjacent the first signal wire at a first offset distance, the first and second shielding wires exerting a first capacitive coupling effect on the first signal wire; positioning third and fourth shielding wires oppositely adjacent the second signal wire at a second offset distance, the third and fourth shielding wires exerting a second capacitive coupling effect on the second signal wire that is greater than the first capacitive effect on the first signal wire such that the signal arrives at the first and second receiving components at nearly the same time.
In another embodiment, a device including a network in which the skew is balanced utilizing coupling capacitance includes: at least one sending component, the at least one sending component for sending a signal over a signal wire to one or more receiving components in a network; a first receiving component communicatively coupled to the at least one sending component by a first signal wire, the first receiving component being located a first distance along the first signal wire from the at least one sending component in the network; a second receiving component communicatively coupled to the at least one sending component by a second signal wire, the second receiving component being located a second distance along the second signal wire from the at least one sending component in the network, wherein in the second distance is less than the first distance; a first pair of shielding wires positioned oppositely adjacent the first signal wire at a first offset distance, the first pair of shielding wires for effecting a first capacitive coupling of a signal carried on the first signal wire; a second pair of shielding wires positioned oppositely adjacent the second signal wire at a second offset distance smaller than the first offset distance, the second pair of shielding wires for effecting a second capacitive coupling of the signal carried on the second signal wire greater than the first capacitive coupling of the signal carried on the first signal wire, such that the signal is received at the first and second receiving components at nearly the same time.
In a further embodiment, a method for utilizing coupling capacitance to balance skew in a network includes: designating a first signal path in a network, the first signal path for carrying a signal from a sending component to a first receiving component in the network; designating a second signal path in the network, the second signal path for carrying the signal from the sending component to a second receiving component in the network, the second signal path being shorter in distance than the first signal path; and effecting a first capacitive coupling effect on the first signal path and a greater second capacitive coupling effect on the second signal path, so that a signal carried on the first and second signal paths arrive at the first and second receiving components nearly simultaneously and balance skew in the network.
In some embodiments, effecting a first capacitive coupling effect on the first signal path further includes: positioning first and second shielding wires oppositely adjacent the first signal path at a first offset distance. In some embodiments, effecting a second capacitive coupling effect on the second signal path further includes: positioning third and fourth shielding wires oppositely adjacent the second signal path at a second offset distance, the second offset distance being less than the first offset distance.
As a result of these and other features discussed in more detail below, methods and devices designed according to the principles of the present invention permit skew in a network to be balanced by varying the speed of a signal in a signal wire utilizing the coupling capacitance of shielding wires oppositely adjacent the signal wire. The present invention does not require the processing complexity and costs associated with the prior art technique earlier described.
It is to be understood that both the foregoing general description and the following detailed description are intended only to exemplify and explain the invention as claimed.